Plant Clones • To a biologist, a clone is a population of genetically identical organisms. • Clones are produced naturally when organisms reproduce asexually. • This happens commonly in bacteria, fungi, insects and plants. • Mitotic cell division, or binary fission in the case of some microbes, ensures that the same genetic information is passed to the offspring. To a biotechnologist: A clone is an exact copy of: DNA A gene A chromosome (or genetic material) A cell The whole organism You will need to differentiate between reproductive and non-reproductive cloning. Reproductive cloning: Produces a whole organism Normal with: Natural cloning Artificial propagation in plants Artificial embryo splitting Somatic cell nuclear transfer in animals Non-reproductive cloning (aka therapeutic cloning): Produces cells or tissues to treat: Genetic disorders Degenerative conditions Damage caused by trauma Plant Clones • Producing plant clones is relatively easy: – Many plants reproduce asexually and so produce clones naturally – Cuttings often ‘take’ easily, i.e. produce roots and grow – Humans have made use of this for many thousands of years • Some of the micropropagation techniques used to artificially produce clones are extensions of these simple techniques. • Others depend upon manipulating conditions so that cells initially just grow, and then are persuaded to differentiate. Plant cloning • There are many examples of natural vegetative propagation in plants producing clones. These include bulbs and corms, tubers, runners, rhizomes and root suckers. Asexual reproduction in plants • A rhizome is a modified stem serving as an organ of vegetative reproduction e.g. Aloe vera • Adventitious buds develop into above ground stems and leaves, forming on roots near the ground surface and on damaged stems (as on the stumps of cut trees). •A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include Elm, Dandelion, Yew and members of the Rose Family. Another type of vegetative reproduction is the production of bulbs. Plants like onion and tulips reproduce by forming bulbs. Other plants like potatoes reproduce by a similar method of producing tubers. Aerial stems, called runners or stolons are important vegetative reproduction organs in some species e.g. strawberry, numerous grasses and spider plants. Runners (stolons) Q. What are the advantages and disadvantages of such vegetative propagation (cloning)? • Consider uniformity; • ability to colonise an area and exclude competitors; • ability to withstand destruction of above ground foliage (by insects, grazers, fire or human activity) • fallback position if sexual reproduction fails • persistence and ability to spread (if a weed) • lack of genetic variation • speed of spread or colonisation of a new area (compared to sexual reproduction and seed dispersal). Advantages • Uniformity – It is likely that it is suited to the area that it is growing in, so all new plants will be equally suited. • Ability to colonise an area and exclude competitors – Suited to conditions and dense growth • Able to withstand destruction of above ground foliage – By insects, grazers, fire or human activity – Regenerate from underground parts • Fallback position if sexual reproduction fails Disadvantages • Uniformity / lack of genetic variation – If conditions change and no longer suited... • Persistence and ability to spread – If it is a weed, it is a disadvantage to the farmer (but an advantage to the weed) • Rapid spread and colonisation of a new areas – Compared to sexual reproduction / seed dispersal Plant Clones • Producing plant clones is relatively easy: – Many plants reproduce asexually and so produce clones naturally – Cuttings often ‘take’ easily, i.e. produce roots and grow – Humans have made use of this for many thousands of years • Some of the micropropagation techniques used to artificially produce clones are extensions of these simple techniques. • Others depend upon manipulating conditions so that cells initially just grow, and then are persuaded to differentiate. Natural Clones in Plants • There are many examples of natural vegetative propagation in plants producing clones. • These include: – Bulbs and corms – Tubers – Runners – Rhizomes – Root suckers Bulbs and Corms • Bulbs are condensed shoots which store food reserves in swollen or fleshy leaf bases – e.g. onions and daffodils • Corms store food reserves in swollen stems – e.g. crocus and gladiolus Shallot (a member of the onion family) A single bulb makes many new bulbs. • In either case, lateral buds can develop and grow into new plants. Stem Tubers • In the potato, lateral buds grow outwards from the stem and then down. • The stem swells as food reserves are laid down. Potato tubers The eyes of a seed potato produce the shoots and roots. Swelling appear at the end of side shoots or stolons. – This only happens at the tip of the shoot, rather than along its length (as happens with rhizomes). Runner • A runner is a specialised stem that grows away from the parent plant. • Where a node touches the ground: – Roots appear – The bud at the node grows – A new plant is produced Strawberry runner Adventitious roots form so the plantlet can obtain water and mineral nutrients and become independent of the parent plant. • Whilst growing, the new plant gets its nutrition from the parent to which it is still attached via the runner. Rhizome • A rhizome is a specialised underground stem that grows horizontally. • The old part of the stem does not die. – It can last for many years. – It is swollen with food reserves. Couch grass Underground stems grow from the main plant, allowing it to produce a dense patch and allow the plant to spread. • The growing tip turns up and produces leaves and flowers. Sucker • Meristematic tissue in the root grows and produces basal sprouts. • Basal sprouts can be: – Close to the parent plant • Produces a dense patch of plants – Some distance away • Allows colony to spread Raspberry Meristematic tissue in the root produces sprouts which allow it to establish in a patch and spread to new areas. • The example of English elm (Ulmus procera) will be considered in more detail later.